1. Field of the Invention
The present invention relates to a vibration reducing structure for a steering wheel in which: a mass is supported inside a steering wheel via an elastic body so as to be movable in a direction of an axis and a direction perpendicular to the axis of the steering wheel; a horn switch is activated by pressing the mass in the direction of the axis; and the mass is allowed to vibrate in the direction perpendicular to the axis so as to function as a dynamic damper.
2. Description of the Related Art
A steering wheel has been publicly known from Japanese Patent Application Laid-open No. 2006-96127, in which an air bag module is elastically supported via a coil spring inside the steering wheel; the pressing of a pad of the steering wheel by a driver compresses the coil spring in a direction of an axis direction so as to activate a horn switch; and an inflator of the air bag module is supported by another elastic body different from the coil spring so as to function as a dynamic damper.
Meanwhile, Conventional Characteristic in FIG. 10 indicates a spring constant of a coil spring in a case where the coil spring is employed for both a horn switch and a dynamic damper. The stiffer the coil spring is, the larger the spring constant in a direction perpendicular to the axis becomes in proportion to an increase of the spring constant in the direction of the axis. A region with diagonal lines indicates a region where the horn switch malfunctions due to vibration because the spring constant in the direction of the axis is too small, and if a soft coil spring is employed so that the spring constants are set at a point A in the region with diagonal lines, the horn switch may possibly malfunction. In order to prevent this, if a stiffer coil spring is employed so that the spring constants are set at a point B outside the region with diagonal lines, the spring constant in the direction perpendicular to the axis becomes higher than the spring constant at a point C which allows the function as the dynamic damper to be effectively fulfilled. As a result, a problem may occur that the function as the dynamic damper cannot be effectively fulfilled. Accordingly, as with the above-described conventional example, if the air bag module is supported with a common coil spring both in the direction of the axis and the direction perpendicular to the axis, there is a problem that a good balance between the function as the horn switch and the function as the dynamic damper cannot be achieved.